Blade fastening



July 17, 1928; 7 1,677,807

BLADE imm Fil ed Nov. 4, 1925 ATTORNEY Patented July 17, 1928.

nnrrsn srA'rEs PATENT OFFICE.

WALTER WESSEL, F LESTER, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELEC- TRIO AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

BLADE FASTENING.

Application filed. November 4, 1925. Serial No. 66,829.

My invention relates to elastic fluid turbines, more particularly to the blading there of and has for its object the provision of improved holding means for the blades where in bending moment-s incidental to the load imposed upon moving blades'by centrifugal force shall be offset.

Apparatus embodying features of my invention is illustrated in the accompanying drawings forming a part of this specification wherein Fig. 1 is a fragmentary sectional view of a blade holding disc with a blade mounted therein in accordance with my invention; Fig. 2 is a sidcelevation of the same; Fig. 3 is a View similar toFig. 1 but showing a different form of blade root, and

, Fig. 4 is a side elevation of the blade shown in Fig. 3.

One main type of conventional blade holding means for moving blades, as known to me, embodies blade roots with off-set portions inserted in complementary slots in the disc, or astride complementary formed surfaces on the disc. In operation, centrifugal force acting on the blades imposes a load on the blade roots which is transmitted to the disc on which it is mounted. Due to the offset portions of the blade roots, the load thereon due to centrifugal force acting against the complementary holding surfaces of the disc, exerts a force in an angular direction which tends to bend the material of the disc or the blade, according to the type of the blade holding means, out of engagement with their cooperating surfaces. In order to overcome this difficulty, it has heretofore been found necessary to add more material to the blade holding disc or the blade root, as the case may be, in order to withstand the bending stress to which it is subjected.

I overcome the before-mentioned ditliculties. in accordance with my invention, by ineluding means for holding the material of the blade and the disc against relative lateral movement. In this way, no additional material need be added to the disc or to the blade root and the bending effort of the blade root is entirely overcome. The means for holding the material of the blade and the disc against relative lateral movement preferably is in the form of a screw interposed between the blade root and the disc. After assembly of the blades on the disc, holes are drilled between the bases of the blades and the discs, the holes are tapped andscrews are inserted in the holes.

Referring now to the drawings for a better understanding of my invention I show in Fig. 1 at a fragment of a blade holding disc having a blade 11 mounted therein. The blade 11 is provided with a conventional form of root embodying two T head sections 12 and 13 inserted in a slot 1.4 in the disc. The T head sections 12 and 18 define portions of the blade root which are in shear and which carry the load imposed by centrifugal force upon the blade root in operation. Due to the centrifugal load imposed upon the T head sections, the side walls of the blade holding disc are subjected to a bending stress tending to force the side walls outwardly. I-Ieretofore in overcoming this bending stress it has been necessary to add additional metal to the sides of the disc which, in turn, required a further increase in the disc dimension on account of the ad ditional centrifugal force due to the added metal. I overcome this bending stress by tapping holes as at 1818 which are formed partly in the base of the blade and partly in the disc and inserting therein tightly fitting screws 1919. In this way, the material of the blade itself, in cooperation with the upper surface of the blade holding disc is utilized to overcome the bending stress due to the load on the blade root and no addi tional material need be added. After insertion of the screws 1919 the surface of the material surrounding the heads thereof is preferably peened over so as to prevent the working out of the screws.

Referring to Figs. 3 and 4 I show my invention as applied to adifiierent form of blade root. In accordance with this modification a blade 20 is provided with a bifurcated root portion 21 which is mounted astride a double T-head section portion 22 of the disc 10. The double T-head portion 22 of the disc 10 provides portions thereof in shear which exert a bending stress on the bifurcated root portion 21 of the blade 20. This bending stress is overcome, in accordance with this modification of my invention, by inserting screws 1919 between theblade root and the disc as described in the previous modification.

From the foregoing it will be apparent that I have devised an improved blade holding means for a turbine blade having blade roots with offset holding portions wherein late al bending of material is minimized.

While I have shown my invention in two forms, it will obvious to those skilled in the art that it is not so limited, but is su ceptible of various other changes and modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

iVhat I claim is: i 1, In an axial flow turbine, the combination of a blade holding disc, a blade mounted thereon, one of said elements having a'slot formed therein and the other element havinterlocking with said slotted element, and a screw threaded between meeting faces of the free end of the slotted section and of the other section, said screw terminating outside of that portion of said other section which is disposed within the slotted section. 2. In an axial flow turbine, the combination of a blade holding disc, a blade mounted thereon, one of saidelements having a slot mg a portion disposed within said slot and formed therein and the other element having a portion disposed within said slot and interlocking with said slotted element, said elements having substantially extending meeting surfaces at the free end of the slotted element, and a screw member inserted'between said elements along said meeting surfaces.

3. In an axial flow turbine, the combination of ablade holding disc, a blade mounted thereon, means forholding the blade in place and against centrifugal force including a T- head section projecting from one of said elements, a forked or bifurcated section on the other member for receiving the T-head section, an axially extending tapped hole being formed on each side of the disc member, partly in the free'end of the bifurcated section and partly in the adjacent portion of the other element, and a screw member inserted in each hole for preventingseparation of the parts of the'bifurcated section. a

In testimony whereof, I have hereunto subscribed my 'name this twenty-ninth day of October, 1925.

WALTER- VESSEL, 

